The control of blood flow in the body is regulated by two competing pathways or cascades: the coagulation cascade and the fibrinolytic cascade. In the coagulation cascade, which promotes blood clot formation, the thrombin enzyme cleaves fibrinogen leading to the formation of a clot comprised of insoluble fibrin mononers. In the fibrinolytic cascade, which promotes clot dissolution, plasminogen is converted to plasmin, which degrades fibrin and thus acts to eliminate fibrin clots. These two pathways are balanced in a healthy body via various promoters and inhibitors of the separate cascades. For example, tissue plasminogen activator (t-PA) is a protein enzyme that promotes the conversion of plasminogen to plasmin. Maintaining a proper balance between the fibrinolytic and coagulation cascades is important in maintaining the blood in an appropriate fluid state in the vasculature while minimizing, via appropriate blood clotting, any blood loss which may occur upon trauma to the body.
TAFI enzymes are proteins that inhibit fibrinolysis by inhibiting the conversion by t-PA of plasminogen to plasmin, thus inhibiting the formation of the plasmin protein that promotes blood clot degradation. Thus, TAFI proteins promote blood coagulation. More specifically, the TAFI protein is a 60 kD glycoprotein present in human plasma, which protein is cleaved by thrombin or a thrombin-thrombomodulin complex to its activated form, a 92 residue activation peptide bearing a catalytic domain. The TAFI protein cleaves C-terminal lysine and arginine from partially-degraded fibrin, thus preventing binding and efficient activation of plasminogen to plasmin. For a review of TAFI proteins and their activities, see Bouma et al., 2001, Thrombosis Research 101: 329–354.
The TAFI protein is also known in the art as plasma carboxypeptidase B (“PCPB”). Carboxypeptidase enzymes are known to hydrolyze carboxyl-terminal amide bonds of polypeptides. More specifically, PCPB hydrolyzes carboxyl-terminal amide bonds wherein the adjoining carboxy-terminal amino acids are Lys or Arg (Eaton et al., 1991, J. Biol. Chem. 266: 21833–21838). The DNA sequence encoding human PCPB and its deduced amino acid sequence are described in U.S. Pat. No. 5,206,161 (see also, U.S. Pat. Nos. 5,364,934, 5,474,901, and 5,593,674). Two naturally-occurring polymorphs of human PCPB are disclosed in U.S. Pat. No. 5,985,562.
In view of their function in inhibiting the fibrinolytic cascade, the baboon TAFI proteins and polypeptides of the invention are useful for treating blood disorders wherein clotting needs to be regulated or promoted, such as hemophilia. The present nucleic acids, proteins and polypeptides are also useful in screening assays for other proteins and factors that can modulate TAFI activity and hence, the fibrinolytic and/or coagulation cascades.